This nonprovisional application claims priority under 35 U.S.C. xc2xa7119(a) on Patent Application No. 2001-373187 filed Japan on Dec. 6, 2001, which is herein incorporated by reference.
1. Field of the Invention
The present invention relates to a distance measuring apparatus, and particularly to a distance measuring apparatus of, for example, a camera, using passive AF sensors.
2. Description of the Related Art
The distance measurement using passive AF sensors is known as a process of imaging a distance measurement object by, for example, a pair of left and right line sensors and calculating the distance of the distance measurement object from the amount of deviation between left and right sensor images obtained by the left and right line sensors. In the passive method, the possibility that the distance of the distance measurement object is erroneously measured is generally high because it is difficult to detect the amount of deviation between the left and right sensor images by calculation of correlation values or the like if the contrast of the sensor image (of distance measurement object) is low. Furthermore, in this specification, data indicating the luminance of each pixel of the sensor image obtained by line sensors is referred to as sensor data, and the sensor data itself for use in calculation of correlation values and the like for calculating the distance of the distance measurement object, or data with the sensor data subjected to special processing (contrast extraction processing, etc.) is referred to as AF data.
Also, a distance measurement method is known in which the sensor area of a pair of left and right line sensors is divided into a plurality of areas (herein referred to as divided areas), and sensor images (AF data) are compared between the corresponding divided areas of the left and right line sensors, whereby the distance of the distance measurement object is calculated for each divided area. In this way, even if distance measurement objects of different distances exist in the distance measurement area, their distances can be individually detected, and therefore it advantageously possible to select an appropriate distance measurement object and bring the object into focus. Furthermore, in the case where distance measurement objects of different distances have been detected, typically, the nearest distance measurement object is brought into focus.
Sensor data or AF data is generated by, for example, integrating for each cell the signals outputted from each cell of the line sensor, but conventionally, the output signals of each cell are integrated simultaneously for the same period of time in the entire area of the line sensor (or within the distance measurement area of the distance measurement object) to obtain the sensor data (AF data) in the gross even if the distance of the distance measurement object is to be calculated for each divided area. Usually, the period of integration is adjusted according to the luminance of the distance measurement object so that a proper contrast can be obtained, but if the sensor data is obtained in the gross, there are cases where problems occur such that making the contrast proper in some portions makes the contrast improper in other portions, and thus the distance of the distance measurement object can be calculated only in part of divided areas. In particular, if there exists a more luminous distance measurement object (e.g., the sun) that is not a main distance measurement object, there are cases where the contrast of the more luminous distance measurement object is given priority to compromise the contrast the main distance measurement object, and consequently the distance of the main distance measurement object is not calculated even though the distance of the distance measurement object is calculated for each divided area.
The present invention has been devised in view of these situations, and its object is to provide a distance measuring apparatus enabling proper sensor data (AF data) to be obtained for each divided area for individually calculating the distance of the distance measurement object, thereby reliably performing the distance measurement of a main distance measurement object in the distance measurement using passive AF sensors, and also reducing the distance measurement time and so on.
For achieving the above-described object, the present invention is directed to a distance measuring apparatus, comprising: a sensor data generating device which forms images of light from a distance measurement object on a pair of line sensors constituted by a plurality of light receiving elements, integrates signals obtained from the light receiving elements for each light receiving element to generate a pair of sensor data, and ends the integration when sensor data of selected areas set as the distance measurement area of the each line sensor satisfies predetermined integration end conditions; a sensor data acquiring device which divides the distance measurement area of the each line sensor into a plurality of divided areas, and acquires the sensor data of each divided area from the sensor data generating device; a distance measurement object distance calculating device which individually calculates the distances of the distance measurement object for each divided area according to the sensor data acquired by the sensor data acquiring device; and a distance measurement object distance determining device which determines the distance of the distance measurement object to be employed in focusing control according to the distances of the distance measurement object for each divided area calculated by the distance measurement object distance calculating device, wherein the sensor data acquiring device sets a plurality of the selected areas each constituted by one or more the divided areas in the distance measurement area, causes the sensor data generating device to start the integration for each selected area and performs in succession processing for acquiring the sensor data of the selected area from the sensor data generating device when the integration is ended, and performs processing for dividing and acquiring sensor data to acquire sensor data of each divided area.
According to the present invention, the distance measurement area is divided into a plurality of selected areas, and sensor data is acquired for each selected area, thus making it possible to acquire proper sensor data at every time while the sensor data acquired for each selected area is not influenced by distance measurement objects in other selected areas. For example, even if there exists a distance measurement object of high luminance that is not a main distance measurement object (distance measurement object of which distance is to be measured), the sensor data for the main distance measurement object can be acquired with a proper value (contrast) without being influenced by the distance measurement object of high luminance, and the distance of the main distance measurement object can be measured suitable and reliably.
Preferably, the sensor data acquiring device selectively performs, depending on the luminance of the distance measurement object in the distance measurement area, one of: the processing for dividing and acquiring sensor data; and processing for acquiring sensor data in gross to sets the entire area of the distance measurement area as the selected area to acquire the sensor data of each divided area in the distance measurement area in gross from the sensor data generating device.
According to the present invention, the following advantage is provided. In the case where the distance measurement area is divided into a plurality of selected areas and sensor data is acquired for each selected area, more suitable and reliable distance measurement can be carried out compared to the case where sensor data is acquired in the gross in the distance measurement area, but there is a disadvantage that extra distance measurement time is required for acquiring sensor data for each selected area (note that if the distance measurement of the main distance measurement object is to be performed reliably in the distance measurement area including a distance measurement object of high luminance that is not the main distance measurement object, the distance measurement inevitably requires longer time compared to the case sensor data is acquired in the gross). On the other hand, some distance measurement objects allow distance measurement to be suitably performed even if sensor data is acquired in the gross instead of dividing the distance measurement area into a plurality of selected areas and acquiring sensor data for each selected area. Thus, whether it is necessary to divide the distance measurement area into a plurality of selected areas for performing the distance measurement suitably and reliably, or acquirement of sensor data in the gross with the entire area of the distance measurement area as a selected area satisfies the purpose is determined according to the luminance of the distance measurement object, and sensor data is acquired by the latter processing if it satisfies the purpose, thereby making it possible to reduce the distance measurement time without contradicting the purpose of performing the distance measurement suitably and reliably.
Preferably, sensor sensitivity of the sensor data generating device is switchable; and the sensor data acquiring device sets the sensor sensitivity of the sensor data generating device at one of low sensitivity and high sensitivity according to the luminance of distance measurement object in the distance measurement area.
According to the present invention, sensor data is acquired in sensor sensitivity of the AF sensor, which is consistent with the luminance of the distance measurement object, whereby more proper sensor data can be obtained more reliably, and the distance measurement can be improved in a suitable and reliable manner.
Preferably, sensor sensitivity of the sensor data generating device is switchable, and if the luminance of the distance measurement object in the distance measurement area is high, the sensor data acquiring device sets the sensor sensitivity of the sensor data generating device at low sensitivity and acquires the sensor data of divided areas constituting the distance measurement area by the processing for dividing and acquiring sensor data; if the luminance of the distance measurement object in the distance measurement area is moderate, the sensor data acquiring device sets the sensor sensitivity of the sensor data generating device at low sensitivity and acquires the sensor data of divided areas constituting the distance measurement area by the processing for acquiring sensor data in gross; and if the luminance of the distance measurement object in the distance measurement area is low, the sensor data acquiring device sets the sensor sensitivity of the sensor data generating device at high sensitivity and acquires the sensor data of divided areas constituting the distance measurement area by the processing for acquiring sensor data in gross.
According to the present invention, the distance measurement object is classified as three levels of high sensitivity, moderate sensitivity and low sensitivity, and whether the distance measurement area is divided into a plurality of areas and sensor data is acquired for each area as a selected area of the AF sensor, or sensor data is acquired in the gross, and whether the sensor sensitivity is set at high sensitivity or at low sensitivity are precisely determined to switch the processing according to the luminance of each distance measurement object, thus making it possible to acquire more proper sensor data and to perform suitable and reliable distance measurement.
Preferably, the sensor data acquiring device sets the entire area of the distance measurement area as the selected area and causes the sensor data generating device to start the integration, and detects an integration period between the instant at which the integration is started and the instant at which the integration is ended to thereby determine the luminance of the distance measurement object in the distance measurement area.
According to the present invention, determination of luminance of distance measurement objects is made according to the duration of integration in the sensor signal generating device, and the luminance of distance measurement objects is determined according to the amount of integration time in this way, whereby the necessity of specialized sensors for measuring the luminance of distance measurement objects is eliminated, and the luminance of distance measurement objects in the distance measurement area can be determined accurately.
Preferably, the sensor data acquiring device sets the sensor sensitivity of the sensor data generating device at high sensitivity, and sets the entire area of the distance measurement area as the selected area and causes the sensor data generating device to start the integration in acquiring the sensor data of divided areas constituting the distance measurement area; if the integration is ended within a first integration period after the integration is started, the sensor data acquiring device determines that the luminance of the distance measurement object is high to switch the sensor sensitivity of the sensor data generating device to low sensitivity and carries out the processing for dividing and acquiring sensor data to thereby acquire the sensor data of divided areas constituting the distance measurement area; if the integration is ended after the first integration period and within a second integration period, the sensor data acquiring device determines that the luminance of the distance measurement object is moderate to switch the sensor sensitivity of the sensor data generating device to low sensitivity and carries out the processing for acquiring sensor data in gross to thereby acquire the sensor data of divided areas constituting the distance measurement area; and if the integration is not ended even after the second integration period, the sensor data acquiring device determines that the luminance of the distance measurement object is low, and allows the integration to be continued until the integration is ended with the sensor sensitivity of the sensor data generating device kept at high sensitivity to thereby acquire in gross the sensor data of divided areas constituting the distance measurement area.
According to the present invention, the processing for acquiring sensor data to be carried out in the case where the luminance of the distance measurement object is low is started, and whether the luminance of the distance measurement object is high, moderate or low is determined according to the duration of integration processing in the processing for acquiring the sensor data, and the processing is switched to processing for acquiring sensor data for high luminance if the luminance of the distance measurement object is high, and the processing is switched to processing for acquiring sensor data for moderate luminance if the luminance is moderate, and the integration processing is continued to acquire sensor data if the luminance is low. Thus, determination of luminance and processing when the luminance of the distance measurement object is low can be carried out at the same time, resulting in improved processing efficiency. For example, if the luminance of the distance measurement object is causally low, distance measurement can be carried out in the amount of time same as that of the distance measurement that does not involve processing for determination of the luminance of the distance measurement object.
For example, the distance measuring apparatus is a distance measuring apparatus to be applied to a camera comprising a photometry device for AE; and if the photometric value obtained by the photometry device for AE is at a level considered as ultra high luminance when acquiring the sensor data of divided areas constituting the distance measurement area, the sensor data acquiring device sets the sensor sensitivity of the sensor data generating device at low sensitivity and carries out the processing for dividing and acquiring sensor data to thereby acquire the sensor data of divided areas constituting the distance measurement area.
According to the present invention, it can be determined that the luminance of the distance measurement object is ultra high luminance according to the photometric value obtained by the photometry device for AE if the luminance is ultra high luminance, the determination of the luminance of the distance measurement object according to the amount of integration time in the AF sensor can be omitted to proceed immediately to the processing for acquiring sensor data for high luminance, thus making it possible to reduce distance measurement time.
Preferably, the sensor data acquiring device sets the plurality of selected areas according to address information added for identifying each light receiving element of the each line sensor, the address information indicating the area of each divided area.
According to the present invention, if the distance measurement area is divided into a plurality of selected areas and sensor data is acquired for each selected area, the divided selected areas are set according to the address information indicating the area of the divided area, whereby the necessity of registering in advance the data for setting the selected areas in memory is eliminated, and thus the memory can be saved.